1. Field of the Invention
The present invention relates to a glow starter, which can be applied to a high pressure discharge lamp.
2. Description of the Related Art
High pressure discharge lamps, such as metal halide discharge lamps are increasingly utilized in lighting fixtures because of their high efficiency and color rendering property in comparison with mercury vapor lamps. The metal halide discharge lamp, however, does not start easily, because it is typically supplied with a low discharge starting voltage or a secondary voltage generated by a ballast, such as that which is usually applied to a mercury vapor lamp. The ballast for the mercury vapor lamp is generally utilized, because it is low in cost and compact. However, the starting voltage of the metal halide lamp tends to be high as a result of impurities, e.g., moisture (H2O), which can easily be included with the metal halide and rare gas when the arc tube is filled. The impurities make it more difficult for a discharge to start. In order to improve the starting, the filling pressure of the rare gas can be decreased. However, when the pressure of the rare gas is reduced, the electron emissive material of the electrodes is vaporized excessively at the beginning of the discharge. As a result, the arc tube is blackened, and its luminous flux is reduced over the lamp""s operation.
To solve this problem, when a ballast for a mercury vapor lamp is used in a metal halide lamp, the lamp includes a starter device including a glow starter connected in parallel to the arc tube. When current from the ballast initially passes through the grow starter, an arc discharge is created. As the arc discharge heats bi-metallic elements in the glow starter, the bimetallic elements touch to directly pass current. This causes the arc discharge to be extinguished and the bimetallic elements cool. When the elements cool sufficiently, they separate, creating a counter-electromagnetic force in the ballast which produces a high starting voltage pulse for the metal halide lamp.
To improve starting, a metal halide lamp may comprise an initial electron generating material, e.g., promethium (147Pm). However, it is difficult to handle and dispose of promethium (147Pm) because it is a radioactive isotope.
Furthermore, Japanese Laid Open Patent Application HEI 1-134848 discloses a metal halide lamp which starts more easily. Such metal halide lamp comprises an ultraviolet ray generator arranged near the arc tube. The generator irradiates the arc tube with ultraviolet rays, so that the metal halide lamp tends to start more easily. The ultraviolet ray generator includes an ultraviolet ray-transmitting vessel made of a borosilicate glass or a silica glass, and a single electrode. Furthermore, the vessel of the generator is arranged near a lead wire which supplies electric current to an electrode of the arc tube. According to the application, ultraviolet rays are generated between the lead wire and the single electrode before the metal halide lamp starts. The metal halide lamp does not have a glow starter in the outer bulb, but has an igniter outside. This metal halide lamp has both the ultraviolet ray generator and the igniter to assist in starting the metal halide lamp.
Furthermore, Japanese Laid Open Utility Model Application SHO 63-3086 discloses generating ultraviolet rays using a glow starter. The glow starter includes a vessel made of a quartz glass or a silica glass filled with mercury (Hg), so that ultraviolet rays are generated by a mercury vapor discharge. The application further discloses that the glow starter vessel is made of soft glass and ultraviolet rays of 297 nm, 302 nm, and 313 nm are generated by the mercury vapor discharge. However, in order to generate ultraviolet rays of 297 nm, 302 nm, and 313 nm, a large amount of mercury may be required, which is not friendly to the environment.
According to one aspect of the invention, a glow starter comprises a discharge vessel, filled with a gas mix including a rare gas. The glow starter transmits ultraviolet rays substantially of about 300 nm or less. A pair of electrodes, which are arranged in the discharge vessel, are adapted and arranged to touch each other as a result of being heated by a glow discharge.
According to another aspect of the invention, a high pressure discharge lamp comprises an arc tube, the glow starter, and an outer bulb accommodating the arc tube and the glow starter.
According to another aspect of the invention, a high pressure discharge lamp apparatus comprises a high pressure discharge lamp. A ballast, which has a rated input voltage of about 100V or about 200V, and supplies a secondary voltage between about 200V and about 220V to the high pressure discharge lamp, is arranged in series between an alternating current supply and the high pressure discharge lamp.
According to another aspect of the invention, a lighting fixture comprises a high pressure discharge lamp apparatus, and a body having a lamp socket and a reflector.